Tightened emission control has brought about a strong demand for higher response to engine low velocity, and thus higher response of a turbocharger has been called for.
When the engine is accelerated, exhaust-gas pressure increased by reducing an opening degree of nozzle vanes in a variable capacity turbine, and thus the number of revolutions of the turbine is increased.
An excessively small opening degree of the nozzle vanes leads to a large leakage loss through clearances between both side surfaces of the nozzle vane and wall surfaces facing the side surfaces, and thus leads to a lower efficiency. Thus, there is a problem that the number of revolutions cannot be increased quickly.
It has quite commonly been known that the efficiency can be improved by reducing the clearance involving the nozzle vane. Unfortunately, the nozzle vanes might be stuck when the clearance is too small when components adjacent to the nozzle vane are thermally deformed by combustion gas.
Prior techniques related to the reduction of the clearance involving the nozzle vane includes Patent Document 1 (Japanese Patent Application Laid-open No. H11-229815).
Patent Document 1 discloses a technique of preventing gas from flowing through a clearance between a nozzle vane 100 and parallel walls 102. More specifically, a configuration of a variable capacity turbine is disclosed in which a nozzle chamber 104 defined by a pair of parallel walls 102 is disposed between a scroll chamber and a turbine wheel, both end portions 106 and 106 of the nozzle vanes 100 facing the parallel walls 102 have a thickness larger than a thickness t1 of a center portion 108, and end surfaces of the both end portions are formed to be parallel to the parallel walls 102 and to have a width t2.